(a) The Field of the Invention
The present invention relates to low viscosity unsaturated polyester resins essentially comprising an unsaturated polyester alkyd and an ethylenically unsaturated monomer copolymerizable with the alkyd. The present invention further relates to the glass fiber reinforced products which may be obtained from said polyester resins by the processes of vacuum injection moulding injection between compled moulds, vacuum moulding, low pressure pressure moulding, filament winding, and application by hand and by spraying, which are conventional for unsaturated polyesters.
(b) The Prior Art
The commercial products called "unsaturated polyester resins" obtained by mixing unsaturated polyester alkyd with a copolymerizable monomer; said known polyester resins however have a higher viscosity than the resins of the present invention, the monomer content and the elastic modulus and heat distortion temperature (HDT) of the hardened pure resin being equal. In other words, the applicant has surprisingly found, and this is an object of the present invention, that it is possible to obtain low viscosity unsaturated polyester resins having a low styrene content, adapted to the production of manufacts by the aforesaid processes which are conventional for unsaturated polyester resins.